The present invention relates to vehicle bumper systems having crush towers for supporting bumper beams on vehicles, and more particularly relates to a tubular crush tower configured to absorb significant impact energy in a sequential consistent manner.
The federal government, insurance companies, agencies, associations, and companies concerned with vehicle safety have established standardized impact tests that vehicle bumper systems must pass. Crush towers are commonly used to support bumper bars on vehicle frames, and often are used to absorb energy during a vehicle impact. Several characteristics are beneficial for xe2x80x9csuccessfulxe2x80x9d crush towers. It is desirable to manufacture crush towers that provide a consistent and predictable impact strength within a known narrow range, so that it is certain that the bumper systems on individual vehicles will all pass testing. Advantageously, a consistent and predictable impact strength lets manufacturers make a safer vehicle and also lets them more precisely optimize the bumper systems to reduce excess weight and to utilize lower cost materials. More specifically, it is desirable to manufacture crush towers that provide a predictable and consistent force-vs-deflection curve, and to provide a consistent energy absorption-vs-time curve, and to provide a consistent and predictable pattern of collapse. This lets vehicle manufacturers know with certainty how much deflection is created with any given impacting force, and how much energy is absorbed at any point during an impact or vehicle collision. In turn, this allows vehicle manufacturers to design enough room around the bumper system to permit a non-damaging impact without wasting space to compensate for product variation and to provide enough support to the bumper system on the vehicle frame. The force-vs-deflection curve has several important ranges at which the crush tower changes from elastic deformation to permanent deformation to total collapse and bottoming out. It is important that these various points of collapse be predictable, so that substantial amounts of energy are absorbed before and during collapse, but also so that collapse occurs before excessive loads are transferred through the bumper system into the vehicle and its passengers.
In addition to the above, bumper development programs require long lead times, and it is important that any crush tower be flexible, adaptable, and xe2x80x9ctunablexe2x80x9d so that it can be modified and tuned with predictability to optimize it on a given vehicle model late in a bumper development program. Also, it is desirable to provide a crush tower design that can be used on different bumper beams and with different bumper systems and different vehicle models, despite widely varied vehicle requirements, so that each new bumper system, although new, is not a totally untested and xe2x80x9cunknownxe2x80x9d system.
Some tubular crush towers are known for supporting bumper beams in a bumper system. In one type, two stamped half shells are welded together. However, this process generates raw material scrap. Also, the welding process is a secondary operation that adds to manufacturing overhead costs. Further, the welded crush towers are subject to significant product variation and significant variation in product impact strength, force-vs-deflection curves, energy absorption curves, and crush failure points.
Accordingly, a bumper system including a crush tower is desired solving the aforementioned problems and having the aforementioned advantages. In particular, a crush tower is desired that provides consistent impact strength, consistent force-vs-deflection curves, consistent energy absorption (elastic and permanent deformation), consistent collapse points and patterns, all of this within tight/narrow ranges of product and property variation. Also, a crush tower is desired that can be made with a reduced need for secondary operations and reduced need for manual labor.
In one aspect of the present invention an energy-absorbing crush tower adapted to support a bumper on a vehicle includes a tube made of a continuous contiguous material. The tube has first and second ring sections connected by an interconnecting section. At least one of the first and second ring sections are heat-treated to a different material strength than the other of the first and second ring sections so that, upon receiving an end impact parallel a length of the tube, the first and second ring sections telescopingly collapse with a predictable and consistent multi-phase deformation sequence. By this arrangement, the crush tower is configured to absorb optimal levels of energy at particular telescopingly-collapsed distances.
In another aspect of the present invention, an energy-absorbing crush tower includes a tube made of a continuous contiguous material, with first and second ring sections connected by an interconnecting ring section. The interconnecting ring section defines a shape different than diameters of the first and second ring sections and defines a frustoconically-shaped ramp so that, upon receiving an end impact parallel a length of the tube, the first and second ring sections telescopingly collapse with a predictable and consistent multi-phase deformation sequence. By this arrangement, the crush tower is configured to absorb optimal levels of energy at particular telescopingly-collapsed distances.
In yet another aspect of the present invention, an energy-absorbing crush tower includes a tube having first and second ring sections connected by an interconnecting ring section that, upon impact in a direction parallel a length of the tube, is configured to cause the first and second ring sections to telescopingly collapse into each other with material of the tube folding back onto itself to form a third ring section between the first and second ring sections during an impact stroke that is longer than a length of the interconnection ring section. By this arrangement, the crush tower is configured to absorb optimal levels of energy at particular telescopingly-collapsed distances.
In still another aspect of the present invention, a method comprises steps of forming a crush tower for a bumper system adapted for attachment to a vehicle, the crush tower including a tube having first and second ring sections connected by an interconnecting ring section. The method further includes forming the interconnecting ring section on the tube to a shape different than the first and second ring sections, and heat-treating one of the first and second ring sections to a different material strength than the other of the first and second ring sections. By this method, upon impact to the bumper system in a direction parallel a length of the crush tower, the first and second ring sections telescopingly collapse into each other with a predictable level of energy absorption.
It is an object of the present invention to provide a crush tower with circumferentially formed grooves that crush and deform in a specific, repeatable, predictable and desired manner and sequence during the impact.
It is an object of the present invention to provide a crush tower made of a single continuous and contiguous material that will crush in a sequential manner.
It is an object of the present invention to provide a crush tower having tube sections, at least one of which is heat-treated to a different tensile strength than other of the tube sections.
It is an object of the present invention to provide a crush tower having tube sections that are configured to telescope into each other during a vehicle impact, rather than collapse like known crush towers where back-and-forth folded walls collapse against each other like an accordion.
It is an object of the present invention to provide a crush tower having tube sections connected by an interconnecting tube section that is frustoconically-shaped, with the frustoconically-shaped tube section leading one tube section into another during vehicle impact.
It is an object of the present invention to provide a crush tower having first and second tube sections connected by an interconnecting tube section, where, during a vehicle impact, the first section telescopes into the second tube section and the interconnecting tube section forms a third section trapped between the first and second tube sections during the stroke of impact, the third section undergoing significant but predictable deformation and energy absorption.
It is an object of the present invention to provide a crush tower having first and second tube sections connected by an interconnecting tube section, where the first and second and interconnecting tube sections telescope together in a predictable and highly repeatable sequential manner.
It is an object of the present invention to provide a crush tower that is highly adaptable to different bumper beams and bumper systems, and that can be modified and xe2x80x9ctunedxe2x80x9d to particular bumper beams and particular bumper systems, and that has predictable outcomes and results from such modifications, such as by modifying it with a heat-treating or annealing processes (e.g. larger annealed areas or annealing for greater changes in properties), modifying it by using thicker or thinner wall materials or by using materials of different hardnesses or properties, modifying it by changing tube length, diameters, radiuses, wall configurations or shape, and modifying it with surface changes.
These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings.